Arc Cooling and Short Line Fault Interruption

Abstract

This paper covers the derivation of two sets of short line fault equations for the maximum rate of rise of recovery voltage (RRRV) characteristic of gas blast interrupters. The assumption that the electrical conductivity is proportional to the heat flux potential leads to a Cassie integral equation for post-arc current, a critical thermal time constant and the first set of RRRV equations. The assumption that the electrical conductivity varies exponentially with the heat flux potential leiads to the Mayr equation and the second set of RRRV equations. For both sets of equations it is shown that the maximum RRRV is (a) approximately proportional to the gas pressure; (b) proportional to the effective nozzle arc length at current zero and the number of series breaks; (c) proportional to temperature dependent coefficients which are functions of gas properties; and (d) inversely proportional to (dI/dt)m where m=3/2 and 1 for the "Cassie" and "Mayr" RRRV equations, respectively. These equations are complementary and serve as "first-order" limits on the interrupting capability of gas blast interrupters.